The present invention relates to a piezoelectric valve for controlling fluid flow through valve ports and, more particularly, to such a valve having a plurality of piezoelectric members.
Piezoelectric valves offer several advantages relative to comparable solenoid valves, a primary advantage being a much lower power consumption which renders the piezoelectric valve suitable for applications where the power consumption of a solenoid valve renders the latter unsuitable. For example, a piezoelectric valve is suitable for battery-powered operation in locations where its operation may be activated remotely by radio signals. The piezoelectric valve, like the conventional solenoid valve, may be used to control fluid flow through one valve port or two valve ports, depending upon the desired application.
The diaphragm of a conventional piezoelectric valve comprises a flexible metal substrate to which a piezoelectric material is attached. A single piezoelectric diaphragm including a metal substrate approximately 0.005 inch in thickness and piezoelectric material 0.007 inch in thickness provides approximately 0.010 inch of travel or excursion between the energized (200 volts D.C.) and de-energized states. Application of higher voltages than are appropriate for the piezoelectric material can result in piezoelectric material fracture or premature failure of the device. Assuming that the single diaphragm is to control two aligned facing valve ports, blocking one port in the energized state and the other valve port in the de-energized state, the diaphragm would include on each face, aligned with an adjacent valve port, a pad of an elastometic material to insure the fluidtight nature of the engagements between the diaphragm and the respective valve ports. Of the 0.010 inch excursion, approximately 0.002 inch at the beginning and at the end of the excursion are "lost" or used to insure engagement of the elastometic material and the valve ports--that is, to insure a fluidtight connection between each pad and its respective valve port. As a result, the usable excursion is limited to approximately 0.006 inch for the diaphragm (0.006=0.010-(2 .times.0.002)).
The significance of the usable excursion of the diaphragm arises out of the fact that geometrically the maximum usable diameter of the valve port cannot exceed four times the effective excursion. More particularly, the area through which fluid flow from the valve port can be controlled is effectively limited by the surface area of the sidewall of an imaginary column created between the open valve port and the adjacent surface of the diaphragm (that is, the surface area of an imaginary column having a diameter equal to the effective diameter of the valve port through which fluid flows and a height equal to the usable excursion of the diaphragm) so that ##EQU1## where D is the diameter of the valve port (and imaginary cylinder), and X is the excursion (and height of the imaginary cylinder).
By way of example, a usable excursion of 0.006 inch corresponds to a maximum valve port diameter of 0.024 inch. Thus, the aforementioned diaphragm having approximately 0.010 inch of total travel is limited to a valve port diameter of 0.024 inch, assuming that the diaphragm was intended to block one valve port at each end of its excursion. Clearly this limitation severely restricts the volume of fluid which can be controlled at practical fluid flow rates by a piezoelectric valve, and the need remains for a piezoelectric valve which will enable a diaphragm to control valve ports of greater cross-sectional area and corresponding flow rates than is possible with conventional piezoelectric valves.
Accordingly, it is an object of the present invention to provide a piezoelectric valve in which the effective usable excursion of the diaphragm exceeds the usable excursion of a conventional piezoelectric valve using a similar diaphragm.
Another object is to provide such a piezoelectric valve in which the effective usable excursion is more than twice the usable excursion of a conventional piezoelectric valve using a similar diaphragm.
A further object is to provide such a piezoelectric valve which is capable of controlling a valve port having a cross-sectional area greater than the maximum cross-sectional area for a valve port in a conventional piezoelectric valve using a similar diaphragm.
It is also an object to provide such a piezoelectric valve which is of compact and sturdy design, inexpensive to manufacture and easy to maintain.